1. Field of the Invention
This invention relates to a system of measurement of the parameters of semiconductors and preferably group II-VI compositions at cryogenic temperatures.
2. Brief Description of the Prior Art
In some areas of semiconductor material technology, the technology is sufficiently mature such that the properties of the material as grown are known and are repeatable from batch to batch. Accordingly, this as grown material can immediately be utilized in the fabrication of devices without further testing. Silicon is a primary example of such a material.
A problem arises with certain semiconductor materials in that the technology is not presently sufficiently mature to assure repeatability of properties from batch to batch. It is therefore necessary that such semiconductor materials be tested on a batch by batch basis. In the case of the very important metal-insulator semiconductor (MIS) structures, it has been necessary to fabricate the MIS structures themselves prior to running the appropriate parameter tests. Such tests have been, for example, capacitance-voltage (C-V) and conductance-voltage (G-V) measurements in order to study the electrical properties of the material in the steady state and storage time/breakdown voltage measurements in order to study the electrical properties of the material in the non-equilibrium state. Clearly, the requirement to fabricate a device in order to measure and test the properties of the as grown material is laborious, time-consuming and uneconomic.
An attempt to overcome this problem was developed by the use of a mercury contact probe whereby MIS measurements on semiconductors could be made without the actual fabrication of the MIS structures. This is set forth in an article of G. Abowitz et al., Rev. Sci. Instrum., 38, 564 (1967). This probe provides rapid and reliable evaluation of semiconductors at room temperature. Nevertheless, for narrow bandgap semiconductors such as, for example, HgCdTe and InSb, which are operated at cryogenic temperatures, meaningful MIS measurements can only be obtained at such cryogenic temperatures, such as about 77.degree. K., the temperature of liquid nitrogen, where the mercury contact probe no longer functions. Attempts have been made to use a "squeezable gate" approach on HgCdTe at 77.degree. K. This is reported in an article of B. W. Abshere et al. in "Manufacturing Science Program for HgCdTe Detector Array:, section 8, report to U.S. Air Force, Wright Aeronautical Laboratories in 1986. However this approach is limited to one spot and one sample in each experimental run and only capacitance-voltage measurements are demonstrated.
It follows that the prior art is presently unable to measure and test the properties of semiconductor materials for use in MIS devices at cryogenic temperatures without actual initial fabrication of an MIS device for testing.